The special gene organization and low copy number of the yeast histone genes make them an excellent system for the study of histone gene regulation and control. With recent advances in DNA transformation in yeast, the yeast histone genes provide a possible model for the generation of histone gene mutants and genetic analysis of histone gene control, histone protein function, and nucleosome assembly. Specific areas of study include (1) the structure of the histone gene mRNAs and their relationship to DNA sequence of the genes. The mRNAs will be analyzed by Northern blot experiments, and by sequence analysis of the individual histone gene mRNAs. (2) The cell division cycle control of histone gene transcription. The rate of synthesis and degradation will be measured as a function of the cell cycle. Cell fractions from cultures in balanced growth and cells in synchronously dividing cultures will be assayed for transcription by pulse-label and pulse-chase experiments. (3) Mutant derivatives of the histone genes will be constructed using the cloned genes. These mutants will be used to transform yeast cells and the phenotypic properties of the strains will be examined. In particular an attempt to delete copies of the histone genes from the genome will be made. Mutants will be shuttled into the genome and screened for conditional mutations. Multicopy episomal plasmids will be used to manipulate the gene dosage of the histone genes as a way of selecting mutants. The regulation of the mutant genes will be examined at the transcriptional level.